I don’t know where sea zone 7 is. I am guessing it is southeast of London.
If you are unloading from a sea zone, all hostile naval units in that sea zone must either be destroyed or submerged before you unload.
The presence of absence of hostile naval units in other sea zones adjacent to the territory you are unloading to make no difference. It makes no immediate difference if the US has twenty battleships southwest of London if you are unloading southeast of London.
So usually if you have a big UK fleet southeast of London, Germany should not try invading, because most of Germany’s navy will die, and there will be very little ground and air left to attack London. At least one transport has to survive the naval battle, because the naval battle takes place BEFORE any units can be unloaded from transports into enemy territory.
Much better in most cases is sacrificing the Baltic fleet and attacking together with Western Europe fighters to decimate the UK navy.
You can either sacrifice the Baltic navy to destroy the UK battleship, or retreat. If retreating, the Baltic fleet will often be destroyed by either the UK battleship plus UK air, or by hit and run by UK followed by US air (this allows the UK battleship to possibly be preserved if UK builds some fodder units, but unlikely if Germany’s air still strong). If the Baltic navy does not retreat (so the UK battleship is destroyed), any Baltic units will probably be destroyed by the US Atlantic fleet along with US air from London.